a final stripe. Each stripe falls on an array of 96 copper wires on 100 pm centers, each 75 pm diameter and 2 cm long. Two such arrays comprise one WISRD.
._
SLAC-PUB-4737 LBL-26243 October 1988
.
U/A)
A CDU-BASED DATA ACQUISITION SYSTEM FOR THE ENERGY SPECTROMETER AT THE STANFORD LINEAR COLLIDER* D. D. BRIGGS AND J. E. TINSMAN Stanford Linear Accelerator Center Stanford University, Stanford, California 94309
F. Lawrence
Berkeley
RousEt
Laboratory,
Berkeley,
California
94720
CHRISTOPH VON ZANTHIER University
of California
at Santa
Cruz, Santa
Cruz,
California
95064
ME
EXTRACTION LINE SPECTROMETER B E A M OPTICAL ELEMENTS (Ebc’m ELS Show)
Abstract .-We describe a system using the Calorimetry Data Unit (a 32-channel multisample analog integrated circuit) to read out the charge ejected by secondary emission of a synchrotron beam from wires lying in its path. The wires comprise the WireImaging Synchrotron Radiation Detector (WISRD) in the SLC Extraction-Line Spectrometer. The primary module in the system is, a board containing 24 channels of charge sensitive ampli. fication, shaping, sampling, multiplexing and digitization. This board also provides a fast analog measure of the charge distribution across the wires. We discuss Ihe design and performance of this system. ..
‘.
Fig. 1. Elements of the Extraction Line Spectrometer Beam Optics (electron beam into the south dump shown).
Introduction
The Wire-Imaging Synchrotron Radiation Detector (WISRD) Readout system provides a novel measurement of the Stanford Linear Collider (SLC) at the Stanford Linear Accelerator Center beam energies on a pulse-by-pulse basis by. measuring distributions of synchrotron radiation in the ExtractionLine Spectrometers (ELS).’ The electron and positron beams leaving the Interaction Point (IP) are steered into ELS beam lines wIGre?ach beam generates a pattern of synchrotron radiation. (See Figure 1.) Each pattern includes an initial and a final stripe. Each stripe falls on an array of 96 copper wires on 100 pm centers, each 75 pm diameter and 2 cm long. Two such arrays comprise one WISRD. The nominal distance between synchrotron stripes is 27 cm and is inversely proportional to the beam energy. The synchrotron radiation ejects charge from the wires. The total charge ejected from the wire array by each.stripe is approximately 180 fC distributed over a few wires for 10” electrons or positrons in an ideal primary beam of zero emittance, width and dispersion.2 (See Figure 2.) Measurement of the mass of the 2’ by the Mark II Detector3 at SLC requires measurement of the beam energies. Compared.to the energy measurement av&ble from the Phosphor Screen Monitors in the ELS, this new technique offers improved resolution, due to its improved acceptance for high energy synchrotron light with lower production angle. The distributions are also of interest to accelerator diagnostics. _- * Work supported by the Department of Energy, contracts DE-AC03-‘76SF00515, DE-AC03-76SF00098 and DE-AMOS76SFOOOlO. t Presidential Fellow, University of California at Berkeley. Presented
at the Nuclear
Science Symposium,
0
20
40
60
60
100
WIRES
::t
Fig. 2. Shown is a Monte Carlo histogram of the charge in arbitrary units as a function of wire number in an army. The above distribution corresponds to an ideal primary beam of zero emittance, width and dispersion. The total charge for a pn’mary beam of 10” electrons or positrons is predicted to be 180 fC. In operation the final stripe is expected to be four to six times wider than the initial stripe, due to dispersion, with the same total charge.
Environment
-
Each WISRD detector is about 600 feet downstream from the IP on opposite sides. They are within a few feet of their respective beam dumps and within inches of the beam pipes which deliver beams to the IP. Access is prohibited during operation and extremely limited by the accelerator schedule in any case. The radiation environment is harsh. Any cabling to the Orlando,
Florida,
November
9-11,
1938
FRONT END ELfXTRONW=S
detector mus; run near the beamline. Therefore, preamplification, shaping and digitization are performed near the detector by several Data Acquisition (DAQ) modules. The major design considerations for these modules were resolution, reliability in a high radiation and electronic background environment, speed and space constraints, and ease of repair given its remote loca_tion. The resulting design achieves good modularity and packing Ylensity by putting 24 channels of readout and digitization per module. The digitized data are sent to CAMAC-based ‘memory located near the counting house of the Mark II detector. Front
End
WISRD
Electronics
The WISRD readout system comprises an RF cabinet next to each WISRD detector connected by a 25-pair cable to a dAMAC-based control and readout crate in a CAMAC branch of the Mark II Detector readout system. Each RF cabinet is stainless steel with continuous Cu-Be leaf spring shielding gaskets in all openings (Equipto Electronics Corporation R3 type EMI/RFI cabinet) and contains a Eurocard crate, a power supply-chassis, fans, EM1 filters on the 115 VAC power, EMI filters on the DC voltages (+5V, f15V, f9V) and common-mode suppressiou on all signals between the RF cabinet, the CAMAC crate’and the detector. The Eurocard crate contains modules described below. Connection to the detector is made by eight cables 20 feet long, each comprising 25 coaxial cables (RG-174), in an overall shield of Zippertubing.@
n Fillal Stripe Arra
The Eurocard crate contains eight DAQ modules, one Analog module and one Calibration/Communication module. Each is of a 6 U double-width format, providing two backplane connectors of 32.pairs each. One backplane connector receives bussed power, calibration and control signals. The other is used for .routing individual iriterconnections. (See Figure 3.) Each wire array is attached to four DAQ modules.
,o-ss
(LeCroy
* summing circuitry to gederate two linearly weighted sums -. using the outputs of the shaping amplifiers.
ADC804 serial output
l2-bit
ADC.
The summing circuitry generates its two weighted sums, a and b, as follows: Given a charge distribution across the subarray of wires associated with a DAQ module, ql,q2, . ..q24.
* a Signetics 828105 FPLS sequencer which coordinates the CDU and ADC and encodes the serial data for transmission. * attenuation and distribution bration lines.
c
CAMAC
The serial data stream from the ADC is processed by the sequencer which forms a message consisting of a leading one bit, 12 data bits, and a trailing parity bit. These bits are then Manchester encoded for transmission. This sequencer also generates the control timing for the CDU readout and ADC conversion.
* an Analytek AN-201 Calorimetry Data Unit3 (CDU): an analog memory which acts as a multi-channel sample-andhold and multiplexer. * a Burr-Brown
to/from
Fig. 3. The Front End Electronics is located iv an RF enclosure near each of two detectors, and communicates with electronics in a single CAMAC crate located near the Mark II Detector, 600 feet away.
The DAQ module block diagram is shown in Figure 4. It contains: * 24 channels of charge-sensitive preamplifiers HQV-820) and shaping amplifiers.
e
6142A2
24
24
for each of four bussed cali-
aa
c kl
The shaping amplifier output peaks at 5 p’s in response to a step-function input, The equivalent noise charge evaluated at the output of theshaping amplifiers is about 1 fC. These outputs couple to the CDU and the weighted sums.
k .a
b a x(25
- k) . qk
.
Ll
The sums from individual DAQ boards are combined by the Analog module to form composite weighted sums, A, and B, (middle) over the central 48 wires, and At and Bt (total) over the entire 96 wires in an array. The ratio A-B/A+B, either over the middle or the entire array, provides a measure of the deviation from the nominal stripe position in each array. The composite sum waveforms are transmitted back to the control room for viewing on an oscilloscope for diagnostic purposes. These signals provide an estimate of the charge yield of the wires and can be used to make a relative measure of the bea.m energies in real time.
On each beam pulse, the CDU takes two sequential samples per channel.. Samples stored in the CDU are read out serially. The output of the CDU is a differential current which is coupled through a differential-current to voltage converter to the ADC. The nonlinearity of the CDU is five percent, as referenced to a line through endpoints of the transfer function over a dynamic range of 300 fC. 2
DATA ACQUISITION MODULE BLOCK DIAGRAM Calibration I 4 I I 1
Current-to-Voltage Converter
-
_ Encoded Serial Data ADC
HOV-820
’ I 1
Shaping
tmu
* c
FPLS (sequencer) Control
I -
-
l-
x24
a Summing Networks
b
Weighted Sums b
10-66 6142A3
b
Fig. 4. The Data Acquisition Module receives signals from 24 w&s in the WISRD array, amplifies and shapes the signals, and stores two samples of each shaped output in a parallel-in, serial-out After data acquisition, the analog samples are analog memory (CDU) on every beam crossing. The Data Acquisition Module also forms two digitized and Manchester-encoded for transmission. weighted sums of the charge distribution on its wires.
CAMAC ELECTRONICS
The Eurocard crate is connected to the CAMAC-based control and readout using the Calibration/Communication module - (in the E urocard crate). The Cal/Comm module receives calibration and control signals and buffers them onto the backplane of the Eurocard crate. It converts the TTL-level messages from the DAQs-into-low-impedance differential signals for transmission back to the CAMAC readout electronics and provides a. ‘local dock for the DAQ module sequencers. CAMAC
Readout
Beam Crossing
-yCrateVorifier
2 Channel Fifo I?
Electronics
The CAMAC crate contains one Timing Generator module, tliio Cable I/O modules and eight Two-Channel FIFO’ modules. Each WISRD requires a Cable I/O module and four TwoChannel FIFOs. The Timing generator is common to both WISRDs: -The Cable I/O modules are connected to their respective cables via a formatting chassis which provides commonmode suppression of all analog and digital signals. (See Figure 5.) Each Cable I/O module interfaces its long cable to associated FIFO modules via front panel LEMO connections and to the Timing Generator via an Auxillary Timing Bus (ATB) on the CAMAC P2 connector. In response to timing signals, the Cable I/O module sends command and control signals to its Cal/Comm module. It also provides a calibration voltage. In a.ddition, it can substitute test data blocks loaded from CAMAC for the data from the DAQ modules for diagnostic purposes. The Two-Channel FIFO module decodes incoming messages and detects erro&-I% response to control signals on the ATB, the data of each decoded message are written into a FIFO memory 16 bits wide by 64 words deep. The data is stored in the lower 12 bits with any errors identified in the most significant four bits.: _ The Timing Generator module accepts a data record written from CAMAC describing a pulse train 16 bits wide and, in response to a beam-crossing signal, asserts the pulse train on the .4TB. The data record consists of up to 1024 pairs of 16-bit words. Of the pair, one word contains the data to be asserted
2 Channel Fifo 2 Channel Fifo 2 Channel Fiio
to/from South Arc (electron beam dump)
1040
6142A4
L
Composite Weighted to Oscilloscope
Sums,
Fig. 5. A single crate of CAhfAC modules services both WISRD detectors. The Timing Generator receives through CAMAC a list describing its cutput sequence. On every beam crossing, it asserts its output sequence on the Auziliary Timing Bus. These signals comprise timing and control for the other CAhfAC modules and, through the Cable I/O modules, to the Front End Electronics. Encoded data from the two detectors are decoded and stored for readout in the two-channel FIFO modules.
-
._
.
and the other word contains a counter value which triggers the output of the next pair. A local 8 MHz clock drives the counter. Results The time between the beam crossing and completion of data acprisition into CAMAC is 1.1 ms providing beam pulse energy measurements at the maximum accelerator repetition rate of 180 Hz for every event logged by the Mark II Detector. Digital message transmission has been exercised, with no message errors in more than 5 x lo6 messages. We have used the composite sum signals to verify a Monte Carlo model of charge yield of one WISRD detector in the beamline. Beam pick-up and other external electronic backgrounds were undetectable. Conclusion The Wire-Imaging Synchrotron Radiation Detector Readout system provides a novel high-resolution, pulse-by-pulse measurement of the Stanford Linear Collider (SLC) beam energies by measuring distributions of synchrotron radiation in the Extraction-Line Spectrometers. Full digital implementation of the system is in progress-and is expected for the resumption of SLC opera.tion in February 1989.
Acknowledgements The authors wish to thank M. Levi and J. C. Kent for their instrumental contributions to the design of this system. We are especially indebted to Juan-Jose Gomez-Cadenas for his Monte Carlo simulation of the physics of the detector, which was vital in understanding the prototype. Thanks are also due to K. Bouldin, A. Keith, M. Petree and D. Wilkinson for their efforts in the prototyping, construction, installation and testing. References Mark II Collaboration
and Final Focus Group, Extraction-Measurement, SLACSLC-PROP(P); Levi et al., Precision Measurements of the SLC Spectrometer Magnets, SLAC-PUB-4654.
Line Spectrometers
for SLC Energy
J.-J. Gomez-Cadenas, SCIPP 88/33, UCSC.
Monte
Carlo
for
the
WISRD,
Abrams et al., The Mark II Detector for the SLC, SLACPUB-4558, submitted to Nucl. Inst. Methods. G. Haller et al., Performance Multi-Channel
Sample-and-Hold
Nucl. Sci. NS-33, 221 (1986).
Report for Stanford/S’LAC Device, IEEE Trans.
_
